reproject_obs is a script that uses
reproject_events to reproject
the event files for a stack of observations to a common tangent point
and then merges them together with dmmerge.
The user may input the location of the new tangent point or
the script will compute a mean value from the input files.

The script also provides diagnostic information based on
the observation configurations since combining observations with
different aimpoints or different CCDs may limit the usefulness of
merged event file.
Finally, the script also manages the auxiliary files for each observation (bad-pixel files,
aspect solutions, etc) by providing either copies or symbolic links to
the files CIAO uses.

reproject_aspect: minimize position differences between two
files

reproject_aspect applies corrections
for translation, scale, and rotation to the WCS of a file.
It compares two sets of
source lists from the same sky region. If three or more
sources are found to be a close match in position, the tool
calculates the transformation that relates the two files and
updates the WCS mapping from SKY(X,Y) to (RA,Dec) either by
modifying the aspect solution or by revising the WCS
keywords, depending on how the parameters are set.

reproject_aspect is actually a script
which runs two tools: wcs_match and
wcs_update. These tools may be run
individually for slightly more flexibility; see the help
files for details.

This tool is the most accurate method of reprojecting a
file, but does depend on source lists for each observation
being available. Note that the source list from the archive
(src2.fits file) is not accurate
enough for use with this tool. Users should create
a new source list by running one of the detect tools; wavdetect is recommended because of its
ability to separate closely-spaced point sources. The
Running wavdetect
thread illustrates how to use the tool.

reproject_events
supports large mosaics that exceed the standard image sizes (ACIS 8k x 8k,
HRC-I 32k x 32k). The data range (FITS TLMIN/TLMAX keywords) are
updated based on the reprojected data. This allows CIAO and
applications like ds9 to make images that cover the entire
range of the data.

reproject_image: match one image to another

reproject_image maps an image in one
WCS reference frame to the WCS of a match image. If a match
image is not available, use reproject_image_grid
instead.

reproject_image has a parameter (method) which
controls whether the input files are summed or averaged
together; "sum" is typically used to reproject the
counts image and "average" is used to reproject the
exposure map when making fluxed images.

reproject_image_grid: project an image to a WCS grid

reproject_image_grid maps an
image in one WCS reference frame to a specified WCS grid.
This tool works similarly to reproject_image, but
does not require a match image.

reproject_image_grid has a parameter (method) which
controls whether the input files are summed or averaged
together; "sum" is typically used to reproject the
counts image and "average" is used to reproject the
exposure map when making fluxed images.

sso_freeze: reproject a solar system object

sso_freeze reprojects the coordinates
in an event file from the frame fixed to the celestial
sphere to the frame of the object. This eliminates the blur
that occurs when an object (e.g. a planet or comet) is
observed moving with respect to the observer. The tool can
also create an object-centered aspect solution file, which
may then be used to generate an exposure map or response
file (ARF) for the data.

Note: using stacks of input files

All of the reproject tools can take a stack of files in the input parameter,
but they do not all handle the stack in the same way. For
instance, reproject_events creates a separate
output file for each item in an input stack, while
reproject_image creates a single merged image from
the stack. Refer to the individual tool help files for
details on how they handle a stack of input files.